Field of the Invention
This invention pertains to constant tension load-transporting mechanisms and, more particularly, to a control for shifting the load between two such mechanisms without effecting a change in the tension on the load. PA3 A pipeline is normally held on a ship, or barge, by a machine or mechanism called a pipe tensioner. The pipe tensioner carries the pipeline in constant tension such that motion of the ship due to sea movement does not cause the pipeline to be damaged by exceeding the tensile strength of the pipeline or bending it so sharply as to cause buckling.
Description of the Prior Art
At certain times in the process of laying the pipeline, it may become necessary to lower the entire pipeline to the bottom of the sea. This may be necessary, for example, because of rough seas. The process is called "abandonment," and the process of picking up the pipeline from the sea bottom is called "recovery."
During abandonment, the pipeline is held in constant tension by the pipe tensioner mechanism or mechanisms. A plug is then secured in the open end of the last section of pipe forward of the pipe tensioner mechanism. To this plug is added a shackle which connects through a wire rope to a constant tension winch.
Since abandonment is normally caused by rough seas, during this condition, there is generally regular, perhaps exaggerated, movement of the pipeline through the tensioner mechanism in order that the tension on the pipeline can be maintained relatively constant. Thus, in attempting to transfer tension from the pipe tensioner to the winch, there is the problem of having two constant tension systems pulling on the same pipeline, with the possibility of instability.